JPS6226323B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to high melt index ethylene polymers, particularly ethylene/α-olefin copolymers having a melt index of at least 100, especially in the range of 100 to 200. Melt index is a measure of melt viscosity that is related to the molecular weight of a polymer. The melt index for the polymers referred to herein is ASTM D-1238.
This is the melt index measured by the method (condition E). The ethylene homopolymer and the ethylene/α-olefin copolymer when the α-olefin is an aliphatic hydrocarbon will be referred to as polyethylene.
Such polyethylenes can be used in a wide variety of end uses, which are dependent, among other things, on the physical properties of the polymer. One such physical property is the polymer's melt index. For example 10
Polymers having a relatively low melt index, especially less than 1, and a density of about 0.915 to 0.960 can be extruded into film form. Such films can be used as packaging materials. Polyethylene can also be processed into molded articles by molding techniques, in particular injection molding techniques. Molding grade polyethylene typically has a higher melt index than that used in film production. The melt index of polyethylene typically used in injection molding processes ranges from about 0.3 to 45, while the density usually ranges from about 0.915 to 0.965. However, 0.1% as α-olefin
Ethylene/α-olefin polymers containing the following butene-1 and having a melt index of 85 and a density of 0.959 are commercially available as injection molding resins. Examples of molded articles that can be produced by injection molding methods are containers used in particular for the packaging of ice cream, yoghurt, margarine and the like. Such containers should be of relatively uniform thickness;
and should have a surface that is acceptable to consumers. The economics of manufacturing containers by injection molding methods depend at least in part on the wall thickness of the container, particularly the minimum thickness compatible with acceptable appearance and physical properties, and the speed at which such containers can be manufactured, such as cycle time. . Small containers tend to have smaller wall thicknesses than larger containers because a lower flow of polymer is required during the injection molding process to fill the mold. The typical wall thickness of containers manufactured by injection molding methods is at least 0.7 mm. For example, smaller than 0.5mm. Attempts to produce containers with low wall thickness have generally been unsuccessful. This is particularly because processing problems result in containers that are incompletely processed, containers with uneven wall thicknesses as a result of processing problems, and/or containers with poor surface appearance. . It is an object of the present invention to provide a polyethylene with improved processability, especially in injection molding processes, and especially for the manufacture of containers having a wall thickness of less than about 0.7 mm. In particular, polyethylenes have now been found that can be processed into containers with reduced wall thickness by an injection molding process and/or have improved flow properties in the molding process. Accordingly, the present invention provides an ethylene polymer having a density in the range of about 0.940 to 0.960, a melt index in the range of 100 to 200, and a ratio of weight average molecular weight to number average molecular weight of less than 5, wherein ethylene and the number of carbon atoms are Provided is an ethylene polymer that is a copolymer with at least one α-olefin that is an aliphatic hydrocarbon having 4 to 10 aliphatic hydrocarbons. In embodiments of the polymers of the invention, the ratio of weight average molecular weight to number average molecular weight is less than 3.5. In a further embodiment, the polymer is an ethylene/butene-1 copolymer. The present invention provides a method for manufacturing a container having a wall thickness of less than 0.7 mm, which is manufactured from a thermoplastic polymer by injection molding the same, wherein the thermoplastic resin has a density in the range of 0.940 to 0.960 and a density of 100 mm. ~
a melt index in the range of 200 and a ratio of weight average molecular weight to number average molecular weight of less than 5; An improved method is provided which comprises using a polymer, ethylene polymer. The ethylene polymer of the present invention is a copolymer of ethylene and at least one α-olefin, which is an aliphatic hydrocarbon and has 4 to 10 carbon atoms. Preferred are alpha-olefins having 4 to 8 carbon atoms, such as butene-1, hexene-1 and octene-1. In a preferred embodiment, the copolymer is ethylene and especially the alpha-olefin is butene-1.
It is a copolymer with only one type of α-olefin when The polymers of this invention have a melt index in the range of about 100-200. In preferred embodiments, the polymer has a melt index in the range of 100-150. The density of the polymers of this invention can range from about 0.940 to 0.960, and is determined primarily by the amount of alpha-olefin in the polymer. When the α-olefin is butene-1, the above density range corresponds to a range of about 0.2 to 2.0 weight percent butene-1 in the copolymer. The density of the polymer is the density determined by the method of ASTM-D-1505. The polymers of this invention are also characterized by a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of less than about 5. Preferably Mw:
The Mn ratio is less than about 3.5. The Mw:Mn ratio can be determined by gel permeation chromatography. The polymers of the present invention can be used in a variety of applications. In particular, the polymers can be used in the manufacture of containers, especially by injection molding techniques. The polymers can be used for producing containers with a wall thickness of less than 0.7 mm, especially less than 0.5 mm, especially less than 0.4 mm. The design of containers made from the polymers of this invention is more critical than the design of containers made from lower melt index polymers. For example, the container may be a "stress point"
-points), for example the junction between the bottom of the container and the wall of the container should be smoothly rounded and free of corners. Such designs will be understood by those skilled in the art. Containers made with high melt index polymers tend to have uniform polymer density and tend to be substantially stress free compared to conventional polymeric containers. The polymer of the present invention is a copolymer and not a homopolymer. Containers injection molded from ethylene homopolymers with densities greater than 0.960 and high melt index tend to be more susceptible to brittleness and cracking when bent. Containers injection molded from the copolymers of the present invention are substantially more resistant to cracking when bent. The high melt index polymer preferably contains antioxidants known for polymers of ethylene. The polymers of the present invention may also contain pigments of the type used for conventional polyethylene. Polymers of the Invention Published on November 17, 1970
It can be polymerized from monomers using methods of the type disclosed in Canadian Patent No. 856137 by WEBaker, ICBSaunders and JMStewart. In such methods, ethylene monomer mixed with alpha-olefin is dissolved in an inert solvent, such as cyclohexane, and introduced into the reaction zone. The monomers are added to the co-ordination catalyst, which is injected separately in a solvent into the reaction zone.
copolymerized in the reaction zone in the presence of a catalyst). Pressure and temperature are controlled so that the polymer formed remains in solution. For example, 40% relative to the reactor field to obtain and control the melt index and/or molecular weight distribution.
Hydrogen can be added to the feed at a rate of ~120 ppm. The polymerization catalyst is normally deactivated as soon as the ethylene copolymer leaves the reaction zone. Catalysts useful in the production of polymers are so-called coordination catalysts. These catalysts include, for example, compounds of titanium or zirconium, preferably compounds in which the metal is bonded to a group such as -oxyhydrocarbon, -halide, or a combination thereof, as an organometallic reducing agent. It can be obtained by mixing with The catalyst used consists of reducing components such as, for example, titanium halides and alkyl aluminums. A preferred catalyst combination is titanium tetrachloride and triethylaluminum or a mixture of vanadium oxychloride, titanium tetrachloride and triisoprenylaluminum. After deactivation of the catalyst, the polymer can be passed through a bed of activated alumina or boxide to remove substantially all of the deactivated catalyst residue. The solvent is then flashed off the polymer;
The polymer can be extruded into water and cut into pellets or other suitable finely divided shapes. The invention will be further illustrated by the following examples. In the example, due to the high flow rate of the polymer
The above except using a weight of 1060g
Measured according to ASTM method. The melt index was then determined from the interpolated calibration curve obtained using a polymer with a melt index less than 100. The unit of melt index is dg/min. Example 1 Ethylene and butene in cyclohexane solution
A mixture of 1 was copolymerized in a commercial scale stirred autoclave reactor in the presence of a catalyst consisting of vanadium oxychloride, titanium tetrachloride and isoprenyl aluminum. Hydrogen was fed to the reactor.
The reaction was terminated using an organic acid quencher and the polymer was then separated from the cyclohexane. Further details of the experiment and the results obtained are shown in Table 1.

[Table] NA = Not measured. However, EI du Pont de
Nemours and Company, Wilmington;
It is believed to have a value of approximately 3.0 obtained by gel permeation chromatography as assayed with university contact resins obtained from Delaware, USA. A sample of the polymer with a density of 0.949 and a melt index of 166 had a Mw/Mn of 3.0. EXAMPLE An ethylene/butene-1 copolymer of the present invention having a density of 0.958 and a melt index of 138 was used to mold containers with a wall thickness of 0.58 mm using a commercial scale high speed injection molding process. Melt temperature was not measured. However, all zone and nozzle temperatures were approximately 55°C, which is lower than that required to process commercial polyethylene with a melt index of 60 using the same mold. Cycle time is approx. per container using commercially available polyethylene.
It decreased from 5.2 seconds to about 4.1 seconds per container using polyethylene with a melt index of 138. The container is a 500ml type used for food packaging.
capacity and had a shape recognized to provide the container with insufficient impact strength, such as an angular lip, stacking shoulder, and base cross section. The container sample was filled with water and the lid was placed on top of the container. The filled containers were dropped base down onto a concrete floor from various heights. The container did not break when dropped from a height of 1.5 m. Additionally, the container sample was placed on a concrete floor and crushed under foot. Only one or two splits of each container were observed. EXAMPLE An ethylene/butene-1 copolymer of the present invention having a density of 0.949 and a melt index of 105 was used to mold containers with a wall thickness of 0.58 mm using a commercial scale high speed injection molding process. Melt temperature was not measured. However, all zone and nozzle temperatures were approximately 55° C. lower than that required to process commercial polyethylene with a melt index of 60 using the same mold. Cycle time was reduced from about 5.2 seconds per container using commercially available polyethylene resin to about 4.1 seconds per container using polyethylene with a melt index of 105. The container has a 500 ml capacity used for packaging food products and has a shape that has been found to impart insufficient impact strength to the container, such as an angular lip, stacking shoulder and base cross-section. Ta. The sample container was filled with water and the lid was placed on top of the container. The filled containers were dropped base down onto a concrete floor from various heights. The container did not break when dropped from a height of 1.5 m. The container sample was then placed on a concrete floor and crushed under foot. No cracks were observed in any of the containers. EXAMPLES Using the method described in the Examples, ethylene and butene-1 were copolymerized to obtain a polymer having a density of 0.959, a melt index of 138, and a Mw/Mn ratio of less than 5.0. The details of the copolymerization method were as follows: Feed: Ethylene 17.8% Butene-1 0.8% Hydrogen 95 ppm Temperature: Inlet 58% Outlet 278°C Ethylene conversion rate 96.4% The obtained polymer was crushed into fine powder. ,and
Dry blended with 1000 ppm talc and re-extruded into pellets. Containers having a wall thickness of 0.36 mm were molded from the pellets using a commercial scale high speed injection molding process using an experimental four cavity mold. The container has a capacity of 500ml,
Insufficient top loading strength
but have a shape that has been found to provide reasonable impact strength, such as having a rounded base section and a fille-ted stacking shoulder. an acceptable container
Molding was performed with a cycle time of 4.0 seconds. The container sample was filled with water, capped, and dropped base down onto a concrete floor. 1m
The F ₅₀ , the height at which 50% of the container was damaged, was obtained. A 30 pound weight was then placed on top of the sample in the container. After 2 hours buckling was observed and after 24 hours all containers were completely crushed. In view of the above, this container is used for a wide range of packaging end uses, such as food and small article packaging.

Claims (1)

[Claims] 1. Ethylene and carbon, characterized in that they have a density in the range from 0.940 to 0.960, a melt index in the range from 100 to 200, and a ratio of weight average molecular weight to number average molecular weight of less than 5. An ethylene polymer which is a copolymer with at least one α-olefin which is an aliphatic hydrocarbon having 4 to 10 atoms. 2. The polymer according to claim 1, which has a melt index in the range of 100 to 150. 3. The polymer according to claim 1 or 2, wherein the ratio of weight average molecular weight to number average molecular weight is less than 3.5. 4. The polymer according to any one of claims 1 to 3, wherein the polymer is a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms. 5. The polymer according to any one of claims 1 to 3, wherein the polymer is a copolymer of ethylene and butene-1.